The invention generally concerns a process and an apparatus for producing hollow bodies from thermoplastic material by means of blow molding.
A typical form of process for the production of hollow bodies from thermoplastic material using the blow molding procedure provides that a preform of a preferably tubular configuration is received by a blow molding mold having at least two blow molding mold portions. The preform is expanded in the closed mold under the effect of an increased internal pressure within the preform. The two portions of the mold are reciprocatable between an open condition in which they are at a suitable spacing from each other and a closed condition in which they define a mold cavity whose contour corresponds to the configuration of the desired expanded preform. The reciprocating movement of the mold portions is produced by a drive system for moving the mold portions between the open and closed positions thereof.
Apparatuses for carrying out such a procedure may be designed in such a way as to have a closing support structure comprising three plates, the support structure having only one drive means for the opening and closing movements of the mold portions. The common drive means is disposed between a first carrier plate which carries a mold portion and a drive plate which is connected by beam members or other suitable connecting members to a second carrier plate which is disposed on the other, remote, side of the first carrier plate. The second carrier plate carries the other mold portion. The consequence of actuation of the drive in the mold-closing direction is that, when a synchronisation element which is fixedly arranged on the main frame structure of the apparatus kinematically connects the mold portions or their carrier plates together in order to implement synchronous movements of the mold portions, the mold portions move symmetrically towards the preform. It may be noted in this respect that the preform may be suspended from the extrusion head of the extruder producing the preform, but it may equally be held in some other fashion, for example by a gripping device.
Triple-plate closing support structures of the above-outlined kind enjoy the advantage of being of a simple, clearly laid-out structure. A considerable contribution to that aspect is made by the fact that the two mold portions only require a common drive for implementing the opening and closing movements of the mold.
An object of the present invention is to provide a process for the production of hollow bodies from thermoplastic material such that the productivity of the operating procedure involved can be markedly increased without an increase in apparatus expenditure in line with the increase in productivity.
Another object of the present invention is to provide a process for the production of hollow bodies from thermoplastic material using blow molding, which affords a fast, rational operating procedure affording enhanced versatility in terms of production engineering and output.
Still a further object of the present invention is to provide apparatus for producing hollow bodies from thermoplastic material, which is designed to provide a higher level of output than previous machines, without a significant increase in the degree of complication of the apparatus structure and accordingly cost.
In accordance with the principles of the present invention, in the process aspect, the foregoing and other objects are attained by a process for the production of hollow bodies from thermoplastic material by means of blow molding of preforms, using a support structure having at least one blow molding mold comprising at least first and second mold portions. The mold portions are reciprocatable between an open condition in which they are at a spacing from each other and a closed condition defining a mold cavity. The mold portions are so reciprocatable by a common drive means engaging a drive plate and a first carrier plate which carries a mold portion, with the drive plate being connected to a second carrier plate carrying another mold portion. At least one further carrier plate is arranged displaceably in the opening and closing direction between the first carrier plate and the second carrier plate. The further carrier plate carries at each of the sides thereof a respective mold portion, while each of the mold portions, with a mold portion carried by a respective adjacent carrier plate, forms a respective blow molding mold. Each of the two blow molding molds thus provided has a means associated therewith and operable to lock the respective mold in the closed condition thereof. The support structure further includes at least one synchronisation means for symmetrically implementing the closing and opening movements of the parts of the respective mold.
Further in accordance with the invention, in the apparatus aspect, the foregoing and other objects are attained by apparatus for producing hollow bodies from thermoplastic material by means of blow molding of preforms, the apparatus including a closing support structure comprising a blow molding mold having at least first and second blow molding mold portions reciprocatable between an open condition in which they are at a spacing from each other and a closed condition in which they define a mold cavity, the mold portions being so displaceable by a common drive means. The drive means engages a drive plate and a first carrier plate which carries one of the mold portions, while the drive plate is further connected to a second carrier plate carrying another mold portion. At least one further carrier plate is arranged displaceably in the opening and closing direction between the first carrier plate and the second carrier plate, with the at least one further carrier plate carrying at each of the sides thereof a respective mold portion, whereby each of those mold portions on the further carrier plate is co-operable with a respective mold portion carried by a respective adjacent one of the first and second carrier plates, thereby to form a respective blow molding mold. Each of the two blow molding molds afforded in that way has a means operable to lock same in the closed condition thereof and the support structure has at least one synchronisation means for ensuring symmetrical implementation of the closing and opening movements of the respective mold.
As will be seen from a detailed description hereinafter of embodiments of an apparatus in accordance with the present invention, for carrying out the process thereof, the operating procedure and apparatus design configuration in accordance with the invention can be summarised, by means of the example of an apparatus having two blow molding molds, insofar as the closing support structure which has first, second and third plates, more specifically the drive plate and the first and second carrier plates, is provided with an additional carrier plate disposed between the two carrier plates. The additional carrier plate carries two mold portions which each co-operate with one of the two mold portions carried by the first and second carrier plates, to afford a respective mold. The two molds formed in that way can be opened and closed alternately by the common drive, with the alternation between the molds being effected by suitable actuation of locking devices by means of which the parts of a mold can be fixedly connected together.
As will become more clearly apparent hereinafter, in that way, by simply doubling the number of molds, it is possible to double the capacity or productivity of the apparatus, without any need to also double other parts of a blow molding apparatus, that is to say for example the drives for the mold portions. As the respective mold which is in the locked condition is connected by way of the at least one additional, freely displaceable carrier plate, to the part of the other mold carried thereby, the locked mold as a closed unit takes part in the opening and closing movements of the respective other mold so that, in spite of the presence of a total of four plates the kinematics of a triple-plate closing support structure are nonetheless retained. Determining that one of the two molds which is opened and closed upon actuation of the common drive means is achieved by suitable control of the locking devices, parts of which can be disposed on the carrier plates.
A corresponding consideration also applies in regard to design configurations with two or more additional carrier plates and thus three or more molds. In all cases, a common drive means can be provided for all the molds of the apparatus, for implementing the opening and closing movements thereof. Closure of the preform at at least one end thereof to constitute a closed body in which the increased internal pressure for expansion thereof can be produced and the step of squeezing off excess material on the exterior of the preform, are also implemented by the common drive means. This means that the locking arrangement associated with each mold can be relatively simple in structure as it is only operative after the mold has been closed.
In addition to the common drive means, it is also possible to provide a drive device which is operative in the last phase of the closing movement of the mold portions and which applies at least a part of the forces required for squeezing off the excess material on the preform and for closing the preform by heat-sealing or welding thereof. This additional drive arrangement is used alternately for all molds so that the arrangement also only has to have one thereof.
It will be appreciated that it is necessary for the capacity of the apparatus which supplies the preforms to be expanded in the molds also to be increased in accordance with the number of molds in the apparatus for producing hollow bodies from the preforms.
Further objects, features and advantages of the invention will be apparent from the description hereinafter of preferred embodiments.